(1) Field of the invention
The present invention relates to a transducer circuit for use with a power amplifier and, more particularly, to an apparatus for maintaining the transducer tuned to the amplifier over a wide range of frequencies.
(2) Description of the Prior Art
It has long been recognized in the electrical engineering field that full advantage of the amplification available from a power amplifier can be obtained only when the input alternating current signal is tuned to the amplifier, i.e., contains no reactive component. Some loads, however, have substantial reactive component. The problem is particularly acute in the case of the acoustic transducers used in sonar apparatus. In the past, it has been the practice to insert a fixed inductance device between the transducer and the amplifier to remove the reactive component from the signal. This system would be adequate if the signal from the transducer remained at a single frequency and, therefore, the signal had an unvarying reactive component. However, such is not the case, since the frequency of the signal generated by such a transducer may vary over a considerable range. Above and below resonance, the reactance is incorrect, thus requiring the amplifier to output more voltage times current than would be required if the reactive component of the load were tuned out. In other words, the use of a fixed inductor, when the signal varies from the frequency for which the fixed inductance was intended, results in a substantial reactive component remaining.
The power is equal to the voltage times the current multiplied by the cosine of the phase angle, while the amplifier must provide the voltage times the current, irrespective of the phase shift. It, therefore, becomes necessary to design the amplifier grossly oversize, if the transducer is to be operated over a wide frequency range.
Some examples of attempts to solve problems of this type are shown in various U.S. patents. The patent of Henze et. al., U.S. Pat. No. 4,930,063 discloses a voltage regulator particularly adapted to A.C. distributed power systems requiring independent voltage regulation at a plurality of frequency responsive power supply modules energized by a power source at a common alternating frequency, which is provided by resonant tuning of the regulator circuit. The patent of Yamamoto et. al., U.S. Pat. No. 4,749,974 shows a double-tuned circuit provided that is of the type using a primary tuning circuit, including first and second resonance coils connected in series. The patent of Slye et. al., U.S. Pat. No. 4,737,116 has to do with an impedance-matching block for multi-pin connectors. The patent of Aoki et. al., U.S. Pat. No. 4,596,044 discloses a combination UHF/VHF tuner with a switching diode placed in series with a VHF high-range peaking coil, so that the coil forms a parallel resonance peaking circuit when high-range VHF signals are received, so that the coil then acts as a series impedance-matching element when a UHF/IF signal is coupled from a UHF mixer stage. The patent of Torres et. al., U.S. Pat. No. 4,339,827 shows a tuning circuitry for a VHF television antenna, which tunes such an antenna for signals that correspond to the TV channel selected and couples those signals to the tuning system of the television receiver. The patent of Umemura et. al., U.S. Pat. No. 4,144,512 describes an AFC voltage superimposing circuit for an electronic tuner, using a plurality of varactors as a tuning element, comprising a plurality of resistors for superimposing an AFC voltage on a tuning voltage and bypass circuit. The patent of Garskamp, U.S. Pat. No. 4,074,216 discloses a receiver tuning circuit in which, without operation of extra switches, a change-over can be made from tuning; the tuning can be made by means of a continuously-varying tuning voltage. The patent of Minami, U.S. Pat. No. 4,020,420 discloses an electronic channel selector, including a plurality of variable resistors, switches, and a voltage memory circuit. The patent of Scharla-Nielsen et. al., U.S. Pat. No. 2,925,477 shows an ultra-high frequency amplifier using input and output tank configurations and coupling elements. The patent of Cushman et. al., U.S. Pat. No. 2,886,788 discloses tuned elements which are used in ultra-high frequency transmitting and receiving equipment. None of these devices can solve the problems addressed by the present invention. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.